Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
1004 am CST sun Dec 8 2013
issued at 1004 am CST sun Dec 8 2013
Main issue for today will be snow chances and wind chill values.
Will worry about the snow issue with this update...and the wind
chill issue with the next update. Observations across much of
eastern North Dakota in west central Minnesota indicate 1sm to 4sm
visibility...due to light snow. Radar is overshooting much of this
snow...but returns are expanding in coverage. We will switch to
vcp 31 and attempt to see what we are missing. Still not expecting
much snowfall accumulation (up to an inch)...but will use the
philosophy that even a little snowfall can be somewhat
hazardous...and expand the higher probability of precipitation northward for today into
Short term...(today through monday)
issued at 345 am CST sun Dec 8 2013
Water vapor shows a 500 mb short wave moving northeast from
Wyoming into Nebraska. This short wave will move east-northeast
into southern Minnesota this afternoon. Moisture with this system
is quite limited but per radars in South Dakota and latest short
range models do expect some light snow to spread into southeast ND/west-central
Minnesota early this morning spreading northeast across most of the forecast
area during the course of the day. It will be quite light and
models indicate steadier light snow and around half inch or so in
west-central Minnesota with more patchy light snow farther north across NE
ND/far northwest Minnesota. Thus went highest probability of precipitation (categorical) in west-central Minnesota
and far southeast ND today with lower probability of precipitation farther north.
Temperatures will warm today with the cloud cover and a bit milder air
coming in. Expect highs to go above zero in all but far
northwestern forecast area. Current wind chill values of 30 to 40
below zero in the Wind Chill Advisory area (nrn 2/3 of forecast area)
will slowly improve so that by 18z and this afternoon all areas will be
out of advisory criteria. Thus will continue with wind chill advection
until 18z but will not hold on after that.
Another short wave moving south through western Saskatchewan will move southeast
into Montana/northwest ND this afternoon and through the area tonight but limited
moisture means more clouds than anything else. Could be some
flurries. Degree of cloud cover is questionable as some clearing
may occur late tonight and allow temperatures to drop off. When temperatures
drop off...enough wind for wind chills to drop off into advection range
again over mostly western forecast area after 06z. But degree of clearing
and temperature drop in doubt and plus with current advisory out will let
dayshift issue a new one if needed late tonight into Monday
Long term...(monday night through saturday)
issued at 345 am CST sun Dec 8 2013
For Monday night a more potent short wave will move south through central
Saskatchewan into the Red River valley. This one will have limited
moisture but with cold air in place...a period of light snow seems
increasingly likely with an inch or less accumulate. Did up probability of precipitation a
little but not go likely quite yet as some some model disagreement
on precipitation area.
This short wave exists Tuesday only to make way for yet another
one which is due to pass through Tuesday evening. Behind it is another
cold shot with 850 mb temperatures falling back into the middle -20s degree c.
So depending on cloud cover should see some lows back in the -20f
range especially in northwest Minnesota.
For Wednesday through Saturday...long wave trough from Hudson Bay to the
Desert Southwest shifts into eastern Canada this period. High
amplitude flow becomes more zonal through the period. Also models
become more progressive with the flow during this extended period.
GFS and European model (ecmwf) were in good agreement at 84 hours. The European model (ecmwf) and GFS
become essentially out of phase by the end of the period. Fast flow
aloft expected this period...so little confidence in timing of short
waves. Upper level jet shifts north of the area by Thursday...so would
expect some moderation in temperatures. The European model (ecmwf) becomes faster and
farther south with cold air than the GFS by the end of the period.
Surprising given the European model (ecmwf) is more zonal solution.
Will continue to remove low probability of precipitation in the northeast zones.
Temperatures tweaked down a degree or so for Wednesday and up two or three
degrees for Friday from yesterdays run.
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 658 am CST sun Dec 8 2013
Concern today is timing the light snow and lowered vsbys/cigs.
Clouds moving in from the south are of the low end VFR range and
expect that to be the case for most of the day...though some
scattered MVFR ceilings possible in far southeast ND into west-central Minnesota up toward
Bemidji. These MVFR ceilings could reach Fargo as well but for now
kept VFR ceilings. Light snow moving into far-bji middle morning then
gfk-tvf late morning-noon time and dvl noon or early afternoon. Went
MVFR visibilities 3-5sm...though a bit lower for Bemidji.
Winds generally south-southeast today turning a bit more southwest
and west tonight..generally 10 kts or less.
ND...Wind Chill Advisory until noon CST today for ndz006>008-014>016-
Minnesota...Wind Chill Advisory until noon CST today for mnz001>009-013>017-